SYNTHESIS AND STEREOCHEMISTRY OF 11-SUBSTITUTED 5,6,7,8,9,10-HEXAHYDRO-6,9-METHANOBENZOCYCLOOCTENES

5,6,7,8,9,10-Hexahydro-6,9-methanobenzocyclooctene is a ring system [related to the backbone of benzomorphan analgesics] where the cyclooctene ring could exist either in a boat or in a chair conformation. Molecular modeling calculations indicated that the boat conformation is the favored conformation when position 11 is substituted by a ketone group, an amino group, or a hydroxy group. NMR shift reagent studies have shown that these same derivatives exist in this boat conformation. The same studies have also demonstrated that chemical modifications of 11C transforming it from a sp2 to sp3 (i.e., reduction of carbonyl to alcohol) give rise to endo derivatives exclusively. Attempts to obtain the exo derivatives by displacement reactions of sulfonates or Ritter reactions were unsuccessful. The only exo derivative obtainable was the 11-exo-amino-5,6,7,8,9,10-hexahydro-6,9-methanobenzocyclooctene, isolated in low yields from the base-catalyzed equilibration of its N-benzylidene derivative.